Transverse Relaxation Time T2 Research Articles

Pore-scale physics of ice melting within unconsolidated porous media revealed by non-destructive magnetic resonance characterization

Melting of ice in porous media widely exists in energy and environment applications as well as extraterrestrial water resource utilization. In order to characterize the ice-water phase transition within complicated opaque porous media, we employ the nuclear magnetic resonance (NMR) and imaging (MRI) approaches. Transient distributions of transverse relaxation time T2 from NMR enable us to reveal the substantial role of inherent throat and pore confinements in ice melting among porous media. More importantly, the increase in minimum T2 provides new findings on how the confinement between ice crystal and particle surface evolves inside the pore. For porous media with negligible gravity effect, both the changes in NMR-determined melting rate and our theoretical analysis of melting front confirm that conduction is the dominant heat transfer mode. The evolution of mushy melting front and 3D spatial distribution of water content are directly visualized by a stack of temporal cross-section images from MRI, in consistency with the corresponding NMR results. For heterogeneous porous media like lunar regolith simulant, the T2 distribution shows two distinct pore size distributions with different pore-scale melting dynamics, and its maximum T2 keeps increasing till the end of melting process instead of reaching steady in homogeneous porous media.

Experimental investigation of CO2 huff-n-puff in tight oil reservoirs: Effects of the fracture on the dynamic transport characteristics based on the nuclear magnetic resonance and fractal theory

CO2 huff-n-puff is a promising method for enhancing oil recovery in tight reservoirs while simultaneously contributing to CO2 geological storage. However, the performance of this method is significantly affected by fractures resulting from hydraulic fracturing and natural fractures. The impact of fracture on oil transport behavior in different pores remains unclear and warrants further investigation. In this study, CO2 huff-n-puff experiments were conducted under induced fracture conditions. A new method for quantifying the relationship between transverse relaxation time T2 and pore radius was proposed by fitting the slopes of the T2 spectrum and the pore size distribution (PSD) curve derived from Micro X-ray computed tomography (Micro-CT). The impact of the fracture on the effective utilization limit was explored, and the fractal dimensions of different cycles were evaluated during CO2 huff-n-puff. The results showed that the oil recoveries of the fracture-free and the fractured samples were 19.97% and 31.16%, corresponding to the effective utilization limits of 1.52 μm and 0.96 μm, respectively. Moreover, based on the fractal characteristics of the whole process of CO2 huff-n-puff, the pore system was divided into micropores (<0.20 μm), small pores (0.20–0.63 μm), intermediate pores (0.63–2.00 μm), and large pores (>2.00 μm). Furthermore, the incremental recovery for each cycle mainly comes from large pores and gradually decreases as the fractal dimension is less than 2.85. The fracture has a significant impact on the migration characteristics of crude oil. The incremental oil in the intermediate pores of the fractured sample, caused by negative convection, was 2.88 times greater than that of the fracture-free sample. Finally, it was found that the gravity effect was more prominent, significantly affecting the remaining oil distributions in fractured reservoirs.

Magnetic interactions in vortex-state nanodisk arrays characterized by gradient magnetic vortex echo

Magnetic vortices have potential applications in the field of spintronics and medicine and studying their magnetic interactions is crucial for future applications. This work introduces a new method based on obtaining the gradient magnetic vortex echo (GMVE) using micromagnetic simulations following a magnetic resonance imaging protocol. The results show that it is possible to characterize the magnetic interaction of arrays of nanodisks, having equal diameter and vortex configuration, as a function of disk separation. This characterization was performed by creating an inhomogeneity in the system through the application of a magnetic field gradient perpendicular to the plane of the nanodisk array. The inhomogeneity allows refocusing the magnetization in a time-controlled way by inverting the sign of the gradient and obtaining the characteristic transverse relaxation time T2∗ from the GMVE that contains the information on the magnetic interaction.

An NMR-based model for determining irreducible water saturation in carbonate gas reservoirs

Unambiguously determining irreducible water saturation Swirr\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\left({S}_{\\rm{wirr}}\\right)$$\\end{document} poses a formidable challenge, given the availability of multiple independent methods. Traditional approaches often depend on semi-experimental relationships derived from simplified assumptions. These methods, originally designed for oil sandstone reservoirs, result in varying Swirr\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${S}_{{\ ext{wirr}}}$$\\end{document} values when employed in carbonate gas reservoirs. Nuclear magnetic resonance (NMR) is the most advanced technique for determining Swirr\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${S}_{{\ ext{wirr}}}$$\\end{document}. While highly accurate, the NMR-based method necessitates the laboratory measurement of the transverse relaxation time T2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\left({T}_{2}\\right)$$\\end{document} cutoff. Laboratory-based T2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{2}$$\\end{document} cutoff determination is resource-intensive and time-consuming. This research aims to develop a robust model for determining Swirr\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${S}_{{\ ext{wirr}}}$$\\end{document} in carbonate gas reservoirs by utilizing NMR well logging measurements and special core analysis (SCAL) tests. Various T2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{2}$$\\end{document} cutoff values were initially employed to compute bound water saturation Sbw\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\left({S}_{{\ ext{bw}}}\\right)$$\\end{document} at different depths to achieve this. Subsequently, the data points T2,Sbw\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\left({T}_{2}, {S}_{{\ ext{bw}}}\\right)$$\\end{document} were graphed on a scatter plot to unveil the relationship between Sbw\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${S}_{{\ ext{bw}}}$$\\end{document} and T2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{2}$$\\end{document}. The scatter plot illustrates an exponential decrease in Sbw\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${S}_{bw}$$\\end{document} with increasing T2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{2}$$\\end{document}, forming the basis for the Swirr\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${S}_{{\ ext{wirr}}}$$\\end{document} model derived from this relationship. Finally, the parameters of the Swirr\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${S}_{{\ ext{wirr}}}$$\\end{document} model were fine-tuned using SCAL tests. Notably, this Swirr\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${S}_{{\ ext{wirr}}}$$\\end{document} model not only accurately yields Swirr\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${S}_{{\ ext{wirr}}}$$\\end{document} at each depth but also offers a dependable determination of the optimal T2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{2}$$\\end{document} cutoff for the reservoir interval.

On the comparison of two NIPAM gel dosimeters with high resolution 3D MRI sequences

Polymer gel dosimeters allow the measurement of a dose distribution in 3 dimensions. Irradiation induces polymerization reactions in the long chains of the gel molecules, which is characterized by a change in the transverse relaxation time T2. Gel dosimetry is mainly advantageous for its high resolution, but can also be expensive. The main goal of this project is to compare two normoxic polymer gel recipes made with NIPAM as monomer. The analysis is based on the quality of the images obtained for a fixed MRI scan time and a comparative cost of analysis of each 1L phantom. The ΔT2 maps are obtained by scanning the gels before and after irradiation with 3D sequences and the DESPOT2 technique is used to reconstruct the T2 maps. The phantoms were irradiated with 8 photon beams of 6 MV with a fixed 250 MU, 4 at two opposite sides of the jar (AP-PA configuration), to obtain 4 dose distributions of 4.7 Gy, 8.9 Gy, 13.2 Gy and 17.3 Gy. The SNR is then determined in the ΔT2 maps in function of the dose step and the concentration of NIPAM in the phantom. The first gel phantom is made with 15% NIPAM and has a total cost of $1561.65, including products and MRI scan costs. The SNR obtained for the 4 dose steps are 10.02, 31.18, 45.12 and 37.54. The contrast between the T2 before and after the irradiation in the 4 regions of dose are 0.45, 0.66, 0.78 and 0.85. The second phantom contained 5% NIPAM, cost 1186.85$ and the SNR obtained are 16.80, 27.08, 30.11 and 26.17 and the ΔT2 are of 0.61, 0.75, 0.79 and 0.77 for the 4 dose steps respectively. The comparison of the two recipes has shown that the increase of NIPAM concentration does not allow a significant increase in image quality for MRI. The recipe with 5% of NIPAM has a lower dynamic range but a better sensitivity at lower dose and is less expensive than the one with 15% of NIPAM. The results also show that by increasing the NIPAM concentration 3-fold, the cost of a 1L phantom increases by 30%.

NMR Self-Diffusion and Transverse Relaxation Time in Bitumen: The Effect of Aging.

In this investigation the dynamics of two types of bitumens with different penetration grade were tested by using dynamic shear rheometry (DSR) and Nuclear Magnetic Resonance (NMR) at unaged conditions, and upon both short- and long-term artificial aging. The gel-sol transition temperature was found to increase with increasing the time of aging treatment. Arrhenius parameters of the viscosity were found, unexpectedly, to be correlated with those of simple liquids, suggesting that the two kinds of systems, although chemically and physically quite different, share the same basic process at the molecular level. The molecular dynamics has been then investigated by NMR Pulsed Field Gradient Stimulated-Echo (PFGSE) and relaxometry (Carr-Purcell-Meiboom-Gill, CPMG, spin-echo pulse sequence) to capture the effect of aging upon dynamics variables such as self-diffusion coefficients D and transverse relaxation times T2 . The translational diffusion at T> of the light molecular components of both types of bitumens was characterized by broad distributions of D which were found independent of the experimental time scale up to 0.2 s. Similarly, T2 data could be described as a continuous unimodal distributions of relaxation times determined both at T< and T> .

An LF-NMR homogeneous immunoassay for Vibrio parahaemolyticus based on superparamagnetic 2D nanomaterials

In this work, a sensitive low field nuclear magnetic resonance (LF-NMR) homogeneous immunoassay, also called magnetic resonance switch (MRSw) sensor, for Vibrio parahaemolyticus (VP) was developed. Superparamagnetic 2D nanomaterial was designed and used as the magnetic probe of MRSw sensor. It was GO@SPIONs&Ab, a composite nanomaterial with many superparamagnetic Fe3O4 nanoparticles (SPIONs) providing a magnetic signal and VP antibody (Ab) specifically recognizing the target VP evenly distributed on the surface of GO. The presence of VP controllably changed the aggregation state of the probe, eliminating the uncertainty of MRSw sensor type, and thus then achieving a regular variation of transverse relaxation time T2 and ensuing quantitative detection of VP. Triple signal enhancement of the MRSw sensor was obtained due to the application of the designed 2D probe, by increasing the number of SPIONs, improving the magnetic intensity and susceptibility, and forming a synergistic effect. Under optimized experimental conditions, VP could be detected with satisfied sensitivity, selectivity, precision, accuracy, and stability, even in turbid real samples. LOQ for VP was 10 CFU/mL. This detection principle is widely applicable, providing an idea for the construction of highly sensitive MRSw sensors.

Low-Field Nuclear Magnetic Resonance Investigation on Early Hydration Characterization of Cement Paste Mixed with Mineral Admixtures

Mineral admixtures (MA), like fly ash (FA), silica fume (SF), and slag (S), are usually added to cement-based materials to improve their compactness and further enhance their mechanical properties, permeability resistance, and durability. In this study, low-field nuclear magnetic resonance (LF-NMR) is adopted to explore the evolution of the early hydration characterization of cement-based materials with MA by testing the transverse relaxation time T2. Meanwhile, the effect of MA on mechanical properties is analyzed by measuring compressive and flexural strength. The results show that, in the early hydration (0–7 days), the T2 distribution shows a trend of gradually moving to a short relaxation time and changes from a double peak to a single main peak. The decrease in T2i (main peak vertex) means that the evaporated water is gradually distributed in smaller pores with more motion constraints. However, the type and content of MA have little effect on T2i. Porosity gradually decreases in the period of early hydration. The addition of MA causes the porosity to decrease, and the order influence is FA &gt; S &gt; SF, i.e., the porosities of cement paste with 0%MA, 10%FA + 10%SF, 10%FA + 10%S, and 20%FA at 7 days are 48%, 44.5%, 40.7%, and 40.2%, respectively. Additionally, the addition of MA to cement-based materials also decreases the early strength, and the influence order is FA &gt; S &gt; SF, i.e., the compression strength values of cement paste with 0%MA, 10%FA + 10%SF, 10%FA + 10%S, and 20%FA at 7 days are 47.8 MPa, 40.1 MPa, 38.6 MPa, and 37 MPa, respectively.

Surface relaxivity estimation of coals using the cutting grain packing method for coalbed methane reservoirs

Low-field nuclear magnetic resonance (NMR) has been widely used to express the pore-size distributions of conventional and unconventional reservoirs. Based on the equation 1T2=ρFs1r, the determination of the surface relaxivity ρ can help to quantitatively convert the transverse relaxation time T2 to pore radius (r). The existing calculation of ρ using NMR requires supplementary and expensive destructive or non-destructive methods, and consolidated cylinders are required as samples to be well tested. However, the operation of multiple drilling projects and the production of many drilling cuttings are barriers to making rapid measurement of the ρ value of the unconsolidated coal cuttings challenging. In this study, an NMR grain packing method is proposed using different coal grains. The surface-to-volume ratio was transformed into the ratio of the derivative of an arbitrary pore volume to its volume, and the governing NMR equation was established by considering only the NMR porosity and T2 distribution. Sphere and cubic-like models were also constructed. The results showed that the coal with different grain sizes had different relaxation responses, and the different assemblies with the same wgrain/wgrain,c also exhibited some relaxation differences, which might be affected by the diversity in grain packing patterns and grain morphology, resulting in the variation in porosity. In addition, the water film distribution on the grain surface and the soluble minerals in the coal contribute to the variation in ρ values by influencing the relaxation properties of the voids between grains and the pores in the grains. The T2 spectrum indicated that the macropores contributed the most to the porosity, owing to the loose grain packing, and the larger grains might not strictly obey the fast diffusion limit. For the sphere-like model, the ρ values of the Ji15 and Ji17 coals were in the range of 19.47–44.04 μm/s and 36.50–46.66 μm/s, respectively; whereas for the cubic-like model, the corresponding ρ values of these two coals ranged from 24.16 μm/s to 54.64 μm/s and from 45.29 μm/s to 57.90 μm/s, respectively. Finally, different methods of ρ calculation are compared, and its potential field application is discussed.

NV-doped microstructures with preferential orientation by growth on heteroepitaxial diamond

For the wafer-scale fabrication of diamond devices, the growth of diamond substrates by heteroepitaxial chemical vapor deposition is the most promising option currently available. However, the transfer of growth and also structuring processes from small homoepitaxial to larger heteroepitaxial samples is not straightforward and requires adaptation. In this study, we present an approach for the fabrication of functional microstructures including pyramids and mesas as well as more complex structures with hollow centers. The associated methods were previously demonstrated by homoepitaxial growth and are now evaluated on heteroepitaxially grown diamond films. After optimizing the growth procedures to ensure a sufficient quality of the bare diamond substrates, precursor structures for overgrowth were fabricated by e-beam lithography and plasma etching. In the overgrowth of nanopillars, a truncated pyramidal shape was achieved. The characterization with scanning electron microscopy revealed the growth of higher-index facets. Nevertheless, photoluminescence spectroscopy reveals localized doping on the sides of the microstructures. In addition, optically detected magnetic resonance reaches a contrast of 6% of one preferred nitrogen vacancy orientation per facet and a transverse relaxation time T2∗ of 96 ns.

The effect of the molecular structure of hydroxypropyl methylcellulose on the states of water, wettability, and swelling properties of cryogels prepared with and without CaO2

Hydroxypropyl methylcellulose (HPMC) belongs to the cellulose ether family that has hydroxyl groups substituted by hydrophobic methyl groups (DS) and hydrophilic hydroxypropyl groups (MS). Herein, the interactions between water molecules and cryogels prepared with HPMC in the presence and absence of a linear nonionic surfactant, as well as CaO2 microparticles, which react with water producing O2, were systematically investigated by sorption experiments and Time-Domain Nuclear Magnetic Resonance. Regardless of the DS and MS, most water molecules presented transverse relaxation time t2 typical of intermediate water and a small population of more tightly bound water. HPMC cryogels with the highest DS of 1.9 presented the slowest swelling rate of 0.519 ± 0.053 gwater/(g.s) and the highest contact angle values 85.250o ± 0.004o, providing the best conditions for a slow reaction between CaO2 and water. The presence of surfactant favored hydrophobic interactions that allowed the polar head of the surfactant to be exposed to the medium, resulting in a higher swelling rate and lower contact angle values. The HPMC with the highest MS presented the fastest swelling rate and the lowest contact angle. These findings are relevant for the formulations and reactions, where tuning the swelling kinetics is crucial for the final application.

Which risk factors determine cartilage thickness and composition change in radiographically normal knees? – Data from the Osteoarthritis Initiative

ObjectiveTherapy for osteoarthritis ideally aims at preserving structure before radiographic change occurs. This study tests: a) whether longitudinal deterioration in cartilage thickness and composition (transverse relaxation-time T2) are greater in radiographically normal knees “at risk” of incident osteoarthritis than in those without risk factors; and b) which risk factors may be associated with these deteriorations. Design755 knees from the Osteoarthritis Initiative were studied; all were bilaterally Kellgren Lawrence grade [KLG] 0 initially, and had magnetic resonance images available at 12- and 48-month follow-up. 678 knees were “at risk”, whereas 77 were not (i.e., non-exposed reference). Cartilage thickness and composition change was determined in 16 femorotibial subregions, with deep and superficial T2 being analyzed in a subset (n ​= ​59/52). Subregion values were used to compute location-independent change scores. ResultsIn KLG0 knees “at risk”, the femorotibial cartilage thinning score (−634 ​± ​516 ​μm) over 3 years exceeded the thickening score by approximately 20%, and was 27% greater (p ​< ​0.01; Cohen D −0.27) than the thinning score in “non-exposed” knees (−501 ​± ​319 ​μm). Superficial and deep cartilage T2 change, however, did not differ significantly between both groups (p ​≥ ​0.38). Age, sex, body mass index, knee trauma/surgery history, family history of joint replacement, presence of Heberden's nodes, repetitive knee bending were not significantly associated with cartilage thinning (r2<1%), with only knee pain reaching statistical significance. ConclusionsKnees “at risk” of incident knee OA displayed greater cartilage thinning scores than those “non-exposed”. Except for knee pain, the greater cartilage loss was not significantly associated with demographic or clinical risk factors.

An NMR study of the role of coir fibers in the hydration and drying of cement paste at early age

Natural fibers such as coir fibers have been increasingly explored as reinforcement in the cementitious composite to promote sustainable and economical construction. However, the in-situ application of this composite presents challenges due to the complex interplay of water behaviors, involving the hydrophilicity of natural fibers, the hydration of cement and the evaporation due to drying. Although these water-related processes play a crucial role in achieving the desired properties, they have been relatively underreported in the literature. This study aims to investigate the role of coir fibers in the water distribution and pore size distribution during the early age (initial 3 days) of cement paste hydration under drying conditions. Accordingly, Nuclear Magnetic Resonance (NMR) methods involving the moisture profiling and transverse relaxation are used to monitor the water distribution and pore size distribution in time but also in space. The samples are made by adding water-saturated coir fibers to the cement paste at different dosages (0, 1%, 2% and 4%). The effects of drying and coir fiber dosages on the samples are evaluated. The results show that drying leads to a moisture gradient and a larger transverse relaxation time T2, i.e., a coarser pore structure near the drying surface. By adding the saturated coir fibers, the moisture gradient caused by drying is decreased and spread out along the sample. As the coir fiber content increases, the water content along the sample and the total water content of the sample increase. As a result, the samples with coir fibers exhibit a lower T2, i.e., a denser pore structure near the drying surface. Coir fibers are shown to eliminate the adverse effect of drying on cement hydration through three effects, including the internal curing, improved water transport and crack control. The results from this study reveal the promising potential of coir fibers for in-situ construction applications.

Permeability modeling of Upper Cretaceous Bahariya Formation rocks, Abu Sennan field, Western Desert, Egypt

The present work aims to describe in detail the petrophysical properties of the Bahariya Formation (Abu Sennan field) through processing the core sample data and finding out the possible relations between permeability and other reservoir parameters such as porosity, specific internal surface, formation factor, and nuclear magnetic resonance to obtain reliable permeability prediction model of the Upper Cretaceous formation. The core samples have a length range of 2–4 cm with a diameter of 2.54 cm. Many petrophysical reservoir parameters were measured, such as permeability, porosity, density, formation factor, and special measurements such as spectral induced polarization, nuclear magnetic resonance, and specific internal surface. The samples cover a wide range of porosity (11.82–23.68 %) and permeability (0.06–133.65 mD). The porosity-permeability relationship indicates the increase of the permeability with porosity increase for the studied samples. The reservoir quality index ranges from 0.02 to 0.78 μm. The flow zone indicator ranges from 0.09 to 3.39 μm where pore throat radius (R35) ranges from 0.10 to 7.40 μm. The reservoir quality index (RQI) and flow zone indicator (FZI) cross-plot show a better understanding of the formation evaluation. The hydraulic flow units are (0.09 μm < FZI ≤ 3.39 μm) and RQI < (1 μm). NMR longitudinal relaxation time T1 range is 1.21–175 ms, NMR transversal relaxation time T2(100) range is 0.70–91.77 ms, and T2(600) range is 0.74–75.86 ms. Models that incorporate porosity and NMR relaxation times will be more accurate and suitable for permeability prediction. Using multiple regression to determine the exponents of the power-law equation and replacing the porosity with the formation factor can improve the permeability prediction for the samples under investigation. The utilizing of NMR in predicting the permeability through a robust model considers an additional value for the Upper Cretaceous rocks in Egypt.

Investigations into Variations in Meso- and Macro-Physicomechanical Properties of Black Sandstone under High-Temperature Conditions Based on Nuclear Magnetic Resonance

The high-temperature environment has a significant deterioration effect on the meso- and macro-physicomechanical properties of rocks. Black sandstone in Chuxiong Yunnan was chosen as the test sample to perform a high-temperature test, a nuclear magnetic resonance (NMR) test, and a uniaxial compressive test (UCT). After high-temperature heating (25°C–1,200°C), the thermally damaged samples were subjected to NMR tests in both saturated and centrifugal states. The transverse relaxation time T2 spectrum distribution and T2 spectrum area were subsequently obtained. The temperature effect of the mesopore structure was investigated by analyzing the changes in porosity. The T2 spectrum cutoff value was determined, and the temperature effect of the movable fluid migration law for rocks was evaluated. The thermal damage constitutive relationship with porosity as the damage variable was determined, and the evolution law of mesopore structure parameters and macroscopic mechanical parameters was discussed. UCT results showed that the mechanical characteristics of black sandstone were obviously degraded by high temperature, and especially the uniaxial compressive strength (UCS) decreased sharply after the temperature exceeded 900°C. NMR results identified 900°C as an inflection point for the mesostructure change. For temperatures lower than 900°C, the improvement of pore connectivity was not obvious. For temperatures exceeding 900°C, the porosity increased rapidly. The porosity had a great influence on UCS, and there was a clear exponential function relationship between the two. The larger the porosity, the smaller the UCS. It showed that it was an effective angle to study the mesopore characteristics and mechanical properties of high-temperature rocks based on the NMR technique.

Fast calibration of magnetic field coils in miniaturized NMRGs from Rabi oscillation of nuclear spins

We propose a fast and accurate method for the in situ calibration of the transverse coils in miniaturized nuclear magnetic resonance gyroscopes based on the Rabi oscillation of hyperpolarized gaseous 129Xe nuclear spins. In contrast to the conventional method based on the free induction decay initial amplitude of different pulse durations, this method circumvents the error introduced by the frequency detuning of the transverse driving field. We experimentally confirm that the accuracy of the calibration is influenced by the longitudinal relaxation time T1, the transverse relaxation time T2, and the magnitude of the transverse driving field B1. Through the numerical simulation of Bloch equations, we show that the behavior of My′ and Mz can be completely specified by two dimensionless quantities a and b, and we provide a ready-to-use selection criterion of b ≥ 24 for choosing the proper B1. By switching the embedded magnetometer into the longitudinal mode, we demonstrate the effectiveness and efficiency of our new calibration method. Finally, we examine the effectiveness of the selection criterion with our new calibration method. This method is expected to improve the authenticity of coil calibration and relaxation measurement in a more efficient way.

Hyperpolarized 129Xe MRI at low field: Current status and future directions

Magnetic Resonance Imaging (MRI) is dictated by the magnetization of the sample, and is thus a low-sensitivity imaging method. Inhalation of hyperpolarized (HP) noble gases, such as helium–3 and xenon-129, is a non-invasive, radiation-risk free imaging technique permitting high resolution imaging of the lungs and pulmonary functions, such as the lung microstructure, diffusion, perfusion, gas exchange, and dynamic ventilation. Instead of increasing the magnetic field strength, the higher spin polarization achievable from this method results in significantly higher net MR signal independent of tissue/water concentration. Moreover, the significantly longer apparent transverse relaxation time T2* of these HP gases at low magnetic field strengths results in fewer necessary radiofrequency (RF) pulses, permitting larger flip angles; this allows for high-sensitivity imaging of in vivo animal and human lungs at conventionally low (<0.5 T) field strengths and suggests that the low field regime is optimal for pulmonary MRI using hyperpolarized gases.In this review, theory on the common spin-exchange optical-pumping method of hyperpolarization and the field dependence of the MR signal of HP gases are presented, in the context of human lung imaging. The current state-of-the-art is explored, with emphasis on both MRI hardware (low field scanners, RF coils, and polarizers) and image acquisition techniques (pulse sequences) advancements. Common challenges surrounding imaging of HP gases and possible solutions are discussed, and the future of low field hyperpolarized gas MRI is posed as being a clinically-accessible and versatile imaging method, circumventing the siting restrictions of conventional high field scanners and bringing point-of-care pulmonary imaging to global facilities.

Control of fluid flow movement in porous medium with NMR-relaxometry method

The possibility of fixing velocities of fluid motion in model porous medium (glass beads) by measuring the transverse relaxation time T2 by spin echo method is shown. The magnetic field gradient arising due to the difference in the magnetic permeability of the fluid and the porous medium causes a decrease in the average time T2, wich makes it possible to fix the fluid motion in the absence of an external magnetic field gradient. The addition of magnetic nanoparticles to the fluid under study increases the dependence of T2 on fluid velocity and increases the sensitivity in determining the permeability of porous medium by NMR-relaxometry. Keywords: porous media, fluid flow, NMR-relaxometry, magnetic nanoparticles.

Контроль движения жидкости в пористой среде методом ЯМР-релаксометрии

The possibility of fixing velocities of fluid motion in model porous medium (glass beads) by measuring the transverse relaxation time T2 by spin echo method is shown. The magnetic field gradient arising due to the difference in the magnetic permeability of the fluid and the porous medium causes a decrease in the average time T2, with makes it possible to fix the fluid motion in the absence of an external magnetic field gradient. The addition of magnetic nanoparticles to the fluid under study increases the dependence of T2 on fluid velocity and increases the sensitivity in determining the permeability of porous medium by NMR-relaxometry. V.V.Maikov, S.V.Zhakov, I.V.Byzov, A.A.Mysik

Cavitation‐Associated Water Evaporation From Porous Media Through In Situ NMR Characterization

AbstractEvaporation of water from porous media is essential for a large variety of applications, whereas the opacity of porous matrix imposes considerable challenges in unveiling complicated phase‐change phenomena. Air invasion was previously reported as the major desaturation mechanism, while cavitation in porous media is not well studied. Herein we characterize the transient distribution and evaporation of water in homogeneous tight porous media with nondestructive nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI). By monitoring the amplitude change of NMR transverse relaxation time T2, we investigate the dynamical pore filling status and water content during evaporation. Interestingly, we find that the T2 spectrum shifts immediately after the evaporation starts, indicating the emptying of big pores from the entire medium. Disconnected void clusters at different depths in the porous medium are also observed from MRI scanning and optical images. These observations indicate the emergence of cavitation across the entire porous media along with the evaporation from open surface. Cavitation occurs when the water is stretched to metastable state by large capillary pressure from the evaporating meniscus. By studying the evaporation from hydrophilic membrane‐separated porous media, we further demonstrate the existence of cavitation‐associated evaporation. The preferential water vaporization from the bottom part can still be found from T2 spectrum analysis and optical imaging even when the water‐permeable membrane cuts off possible air invasion. Our findings confirm cavitation‐associated evaporation is one of the primary mechanisms for tight porous media, which provides valuable guidance for evaporation and moisture control.